The present invention relates to a cooling apparatus of an optical device used as an illumination device of for example a liquid crystal projector or other display device and to a projection type display device.
A liquid crystal projector is a projector device using a spatial light modulator using a liquid crystal material (hereinafter referred to as a “liquid crystal panel”). In a liquid crystal projector, the liquid crystal panel per se does not emit light. Therefore, in a liquid crystal projector, a light source is combined with the liquid crystal panel to emit light to illuminate the liquid crystal panel. A video signal is applied to the liquid crystal panel to form an image by the liquid crystal panel which is then projected to a screen by a projection lens. A liquid crystal projector having such a configuration enables realization of a small sized, efficient projector device.
Since a liquid crystal projector focuses high energy light of the light source on to the liquid crystal panel through an illumination optical apparatus including a fly eye lens or a relay lens system and projects the image formed by the liquid crystal panel by a projection lens, various locations become high in temperature. For this reason, in a display device such as a liquid crystal projector, a cooling apparatus is provided for cooling the liquid crystal panel, circuits, light source lamp, power supply, and other parts becoming high in temperature in the device.
In general, a cooling apparatus for a liquid crystal projector or other display device measures the temperature of the high temperature parts using a temperature detection sensor, calculates a voltage to be supplied to a fan from the temperature or a temperature difference so as to obtain rotation of an electric fan required for cooling that temperature, converts the calculated result from a digital to analog format, and supplies the voltage to the electric fan through an amplification circuit (see for example Japanese Unexamined Patent Publication (Kokai) No. 4-60534).
In the above system, however, a voltage A′ actually supplied to the fan for the calculated result A ends up being affected by the digital-analog conversion circuit and the amplification circuit, so has error. For this reason, the past cooling apparatus has the disadvantages of a large wasteful consumption of power and generation of noise. In order to eliminate this error, in the art, processing has been performed to sense the speed of the fan and feed it back so as to obtain the desired speed, but this was disadvantageous in that the system ended up becoming relatively large.
It is therefore desirable to provide a cooling apparatus able to operate a cooling fan with the required lowest limit of speed and able to suppress power consumption and generation of noise without inducing an increase of a system size and to provide a projection type display device using the same.